1. Field of the Invention
This invention relates to a method of and apparatus for nuclear magnetic resonance (NMR) testing an object. The invention has particular application to the generation of images of animals or humans by NMR.
2. Related Art
NMR imaging techniques are well-known. One such technique is described in a paper entitled "Planar Spin Imaging by NMR", P. Mansfield and A. A. Maudsley (J. Magn. Resonance, 27, pp 101-119). Another technique is Known as the "Echo Planar Imaging" (EPI) technique, and is disclosed in United Kingdom Patent No. 1596160 to the National Research Development Corporation (now British Technology Group Ltd.). This technique involves subjecting the object to be tested to a magnetic field which Includes three mutually orthogonal gradient components for encoding spatial Information about the object. One of the gradient components has an oscillatory waveform. A radiofrequency excitation pulse is applied to the object in the presence of the magnetic field. The oscillating gradient causes resonance response echoes to be formed subsequent to the application of the excitation pulse. Detection of these echoes rapidly yields an Image of the object.
The EPI technique suffers from the drawback that the oscillating gradient component is required to oscillate at a frequency so high that special and expensive hardware is required to effect the requisite rapid gradient switchings.